The present invention relates generally to heat exchange systems, and more particularly to a self-powered and self-contained heat exchange system having application in, among other things, a high speed civil transport flight vehicle.
It is general knowledge in future heat exchangers involving high Mach number engines, such as engines for a commercial SST (SuperSonic Transport), to cool engine combustor walls for reasons of combustor material selection and NOX (nitrogen oxide) reduction and to cool engine turbine cooling air for reasons of turbine material selection. It is further known to let the heat sink for this cooling be the fuel consumed by the engine. This can be achieved with conventional single heat exchanger designs which circulate cooling fuel past hot outside combustor walls (and which are similar to present aircraft heat exchangers which use liquid fuel as the heat sink to cool engine oil). However, such heat exchangers may be objectionable. Fuel leakage through the walls of the fuel-cooled combustor into the combustion chamber can develop localized thermal conditions (often referred to as hot streaking) which are detrimental to the engine high pressure turbine located downstream of the combustor. Also, leakage of fuel through the turbine cooling air duct wall may cause a fire which would be destructive to the engine.
It is also general knowledge in future heat exchange systems that it may be desirable to use a first heat exchanger to cool the hotter combustor wall or the hotter turbine cooling air with an inert fluid, such as helium (other heat transfer fluids such as steam or gaseous fluorocarbons may be used in other applications), and then to transfer thermal energy from the inert fluid to the colder fuel in a second heat exchanger located outside the combustor region. These heat exchange systems interconnect the two heat exchangers by using a secondary cooling circuit having a portion positioned near the hot temperature region (e.g., a combustor wall) to help define the first heat exchanger and having a portion positioned near the cold temperature region (e.g., a fuel flow region) to help define the second heat exchanger. It is known to circulate helium around the secondary cooling circuit by a heat exchange system compressor driven by some power source.
Common power sources to drive heat exchange system compressors include electric motors and auxiliary power shafts connected to a flight vehicle gas turbine engine. Such power sources ultimately derive from the flight vehicle engine which operates less efficiently when some of its power is diverted from propelling the flight vehicle to driving a heat exchange system compressor. Other power sources include air bled from an engine compressor to drive a heat exchange system turbine which is connected by a drive shaft to the heat exchange system compressor to define a turbocompressor. Use of such bleed air decreases engine efficiency. For these and other such applications, containment of the inert fluid within the secondary cooling circuit introduces the problem of fluid leakage through the seals associated with the pumping devices used to circulate the inert fluid in the secondary cooling circuit.
It is known, as in a household refrigerator heat exchange system, to hermetically seal a compressor and its electric motor inside a housing from which only the motor electric wires extend. This arrangement prevents refrigerant gas leaks, but electric motors are unable to drive pumps which are capable of transferring large amounts of heat, as is required for supersonic flight vehicle applications.
It is also known, as in an automobile radiator heat exchanger system, to drive a water pump from an auxiliary power shaft off the engine. This arrangement is capable of transferring larger amounts of heat than the household refrigerator arrangement, but the water pump is prone to leak in the seal region of its power shaft.
What is needed is a heat exchange system capable of transferring large amounts of heat from a hot temperature region of a supersonic flight vehicle to a cold temperature fuel region of the vehicle without leakage of the heat transfer gas from the secondary cooling circuit and without utilizing power from, or decreasing the efficiency of, the flight vehicle engine.